This invention relates generally to a medium feed mechanism for a printer and, in particular, to a medium feed mechanism capable of performing a plurality of different lengths of micro feeding steps in increments of less than 1 mm.
There are two methods currently employed for the purpose of feeding a medium, such as a paper, card, sheet, film, or the like, in incremental steps of less than 1 mm. The first method is illustrated in connection with the drive mechanism shown in FIGS. 12 and 13. Medium feed roller 51 is supported on and secured to shaft 52 and is driven by the gear engagement of ratchet mechanism 50 which is actuated by a drive mechanism in the form of medium feed electromagnet 53 according to the set medium feed pitch. However, in this method, the precision of feeding a medium in micro incremental steps is dependent upon the precision of gear engagement parts 50A and 50B of ratchet 50, which are illustrated in the inset shown in FIG. 13. Furthermore, medium feeding corresponding to printing more than 50 dots per second is difficult. Also, when feeding a plurality of different types of mediums in the same printer, a corresponding number of drive mechanisms in the form of ratchets 50, i.e., at least one for each medium, are necessary together with medium feed electromagnets 53 thereby rendering the entire printer mechanism of large size with a multitude of complicated moving parts, resulting in a high cost printer.
The second method is illustrated in connection with the drive mechanism shown in FIG. 14. Medium feed roller 57 is supported on and secured to shaft 56 and is driven by step motor 54 via coupled gear train 55 providing speed ratio reduction to match or correspond to the desired medium feed pitch. This combination of components shown in FIG. 14 is employed relative to each particular medium feed mechanism so that when a printer is provided with a capability of printing on a plurality of different types of mediums, a corresponding number of drive mechanisms in the form of gear train 55 along with step motor 54 is necessary thereby rendering the entire printer mechanism of large size with a multitude of moving parts, resulting in high cost printers.
It is an object of this invention to provide a compact, simple structured micro medium feed mechanism capable of performing a plurality of independent micro medium feeding functions as well as providing a selected medium feeding increment less than 1 mm employing a single drive means, e.g., a step motor.